Re: Q: Disk drives for //c...

[Steve Jensen <sjensen@primenetyourknife.com>]

The following is an info file from my old bbs.  I have not done these
mods so procede at your own risk.
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Subj: Duodisk Modifications
 
There are TWO modifications that should be made to Duodisk drives.
 
The first one was recommended by Apple perhaps 5-6 years ago, to 
solve occasional problems with trashing diskettes by Duodisks.  
The solution is to remove 2 capacitors.  The 2nd modification is 
only required for Duodisks to be used on Apple IIGS's (though the
modified Duodisk will still work fine on older Apple II's).  
It requires removing a resistor.  The problem is that the Duodisk
draws just a little too much current. This problem is especially 
apparent when several drives are daisy-chained from the GS Smartport.
Problems are MOST likely to occur when the Duodisk is daisy-chained 
from a Unidisk 3.5 Drive.
 
DUODISK MODIFICATION - REMOVAL OF CAPACITORS
 
OK, here's the first modification for the Duodisk drive.  This mod 
should be done on ALL Duodisks, no matter whether they're used on 
//e's, IIGS's, etc.  The problem was that diskettes would sometimes 
be damaged when doing an Open-Apple-CTL-Reset, or when using disks 
with certain kinds of copy protection.  The mod was in an Apple dealer
service bulletin several years ago.
 
Here's an excerpt from the bulletin, describing the problem:
 
  "Data on disk is damaged when using "Open-Apple-CTL-Reset" for
rebooting,  or when using software with certain copyright protection 
schemes.  Analog board PN is 676-[]101 or 676-[]102."
 
The Analog board is the one inside Drive 1 in the Duodisk.  You may 
have to unplug the cable near the back right of the board to see the
board's model number.  Anyway, if you have the -101 or -102 board, just
break off or cut out Capacitors C29 and C30 (at board locations A1 and 
B1, respectively).
 
DUODISK MODIFICATION - RESISTOR REMOVAL
 
Here's the second modification for your Duodisk drive.  This is the exact
message as posted on Compuserve in 11/86 by an Apple Computer employee:
 
**********************************************************************
 
Duodisk Mod                13-Nov-86 1150               Accesses: 12
 
    This file describes how to modify your duodisk for safe use on the GS.
    Obviously, it is preferable that you have it done by the dealer, but
if
    you want to do it yourself here's the info...
 
Using the DuoDisk with the Apple IIGS
 
The DuoDisk can not be used as the last daisy chained device on the
built-in IWM disk port of the Apple IIGS. For instance, a UniDisk 3.5
will be rendered inoperable when the DuoDisk is installed in the above
manner - although using the DuoDisk by itself is not a problem.
 
A qualified technician will have to modify the DuoDisk analog
board if the DuoDisk is to be used as the last device on the
chain. Please use the following procedure to determine how to
modify the analog board.
 
IDENTIFYING WHICH ANALOG BOARD YOU HAVE
 
Remove the top cover as documented in Technical Procedures. Turn
the drive so that the identifying number will be at the bottom left
of the analog board. The number might read 676-[]101, 676-[]102 or
676-[]107.
 
PERFORMING THE MODIFICATION
 
If the I.D.# for the analog board is 676-[]101 or  676-[]102, use
a pair of nippers and cut out resistor R8 (located at position A2).
 
If the I.D.# for the analog board is 676-[]107, use a pair of
nippers and cut out resistor R39 (located at position A1).
 
eof
 
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